Research into improving cellular wireless communications have traditionally focused on improving capacity and coverage. One technique to improve capacity is for a user equipment (UE) to send a single transport block repeatedly in multiple consecutive subframes. When the network schedules these multiple consecutive subframes with a single resource grant to the UE, this reduces control signaling overhead because there is only one set of signaling messages for the whole transmission. In the evolved Universal Mobile Telecommunication System (UMTS) Terrestrial Radio Access (E-UTRA, also referred to as Long Term Evolution or LTE) radio access technology, this transport block is sent from the Medium Access Control (MAC) layer and the scheduling technique is known as transmission time interval (TTI) bundling. TTI bundling is a particularly efficient technique to improve coverage at the cell edge for voice-over Internet Protocol (VoIP) communications. In the LTE system the TTI is normally 1 ms, and the uplink allows groups of four TTIs to be bundled as mentioned above.
But the 3GPP specifications (for example, series TS 36.321 and 36.213) do not address how the UE should handle colliding TTI bundles. The network access node, known in LTE as an eNB, can send UL grants to the UE which are colliding with TTI bundling that the UE has already initiated. These colliding TTI bundles also impact the synchronous uplink Hybrid Automatic Repeat Request (HARQ) signaling. Services such as VoIP that involve a semi-static packet rate may be scheduled by the eNB via semi-persistent scheduling so as to reduce the control signaling overhead even more. But if the uplink semi-persistent scheduling interval is not evenly divisible by the TTI bundle size, then this also undermines the synchronous uplink HARQ.